Motor Lateralization Research Articles

The H-reflex recovery curve from the wrist flexors: lateralization of motoneuronal excitability in relation to handedness in normal subjects.

Spinal motor asymmetry was studied in relation to handedness. Hand preference was assessed by Oldfield's Questionnaire and Geschwind scores. hand skill was evaluated by a peg moving task. The motoneuronal excitability was assessed by the size and recovery curve of the H-reflex elicited by stimulation of the right and left median nerves. H-reflex was recorded by cup electrodes placed over the wrist flexors. The mean reflex latencies from the right and left sides were 23.4 and 23.2 ms, respectively. The mean amplitude of the maximum H reflex was significantly higher on the right side than the left side in right-handers without familial sinistrality (FS). There were no significant side differences in the amplitudes of H-reflexes of the right-handers with FS. A genetic factor was suggested to involve this left shift of spinal motor lateralization in right-handers with FS. The recovery curve studies showed that the motoneuronal excitability was higher on the right than the left in right-handers without FS. There was no excitability difference between the right and left sides of the right-handers with FS. In left-handers, the motoneuronal excitability was significantly higher on the left than the right side. Voluntary flexions of the wrist increased the H-reflex especially on the right side of the right-handers. There was no relationship between this corticospinal facilitation and baseline EMG activity. The H-reflex amplitude was found to be inversely correlated with hand skill in right-handers. It was concluded that motoneuronal excitability is associated with handedness and also depends on FS. It was suggested that small reflexes are especially suitable in fine motor control of rapid aimed-movements, as the well-established relation between the size of motor units and fine motor control.

Handedness, footedness, and eyedness.

There is no agreement in the literature on whether there are associations among handedness, footedness, and eyedness among normal populations. These need to be clarified before studying abnormal populations. The majority of people have a right-sided preference for each of the three measures of laterality and hence some association is to be expected due to chance alone. Using three categories of laterality a statistical method which is new to these sorts of data has been used which allows the observed percentage agreement to be compared with that expected by chance for all three measures together (as well as in pairs). Its application to data from a sample of 192 young naval recruits suggests that there probably is a generalised dimension of motor laterality, at least among males.

Sensorimotor laterality in schizophrenia: which features transcend cultural influences?

A battery of performance tests was conducted to compare motor laterality and eye dominance in Nigerian schizophrenics and normal controls. Both groups were similar in age and sex distribution. While no difference emerged with regard to right, mixed, or left handedness, or foot or eye dominance, cross-dominance (i.e. full left eye dominance and full right handedness) significantly differentiated the 2 groups. The same feature differentiated paranoid from nonparanoid subtypes of schizophrenia. Cross-dominance may represent a more reliable measure of sensorimotor lateralization in schizophrenia since it may be less likely that it is masked by cultural factors.

Lateral asymmetry in finger localization for right-handed, kindergarten girls.

Laterality in finger localization (FL) was examined in 49 right-handed, kindergarten girls also administered tasks assessing verbal-receptive ability and manual dexterity. A right-hand advantage was evident overall and varied by FL task. The magnitude of asymmetry in FL was not unequivocally related to task requirement for verbal processing and was otherwise independent of children's verbal-receptive ability and motor laterality. The results were discussed in terms of cortical maturation and emergent cognitive-verbal processes as factors to be considered in the interpretation of asymmetry in FL.

Motor lateralization in manic males.

A handedness test, administered to 88 manic male patients and 86 male control subjects, showed no difference between the two groups. The result suggest that unlike schizophrenia, mania is not associated with increased left and/or mixed-handedness.

Lateral asymmetry of the Hoffmann reflex: relation to cortical laterality.

Lateral asymmetry of the Hoffmann reflex (H-reflex) recovery curve was found in seven subjects with no personal or family history of neurological or psychiatric disorder. Differences between recovery curves from the right and left leg were larger than differences in the same leg on two successive test days. In a group of 27 psychiatric inpatients, lateral asymmetry of the later portion of the recovery curve was correlated with cortical laterality, as measured by selective identification of differing verbal stimuli presented simultaneously to both ears (DL) and to total laterality scores, a sum of visual half-field, DL, and motor laterality scores. Asymmetry of the recovery curve is related in part to cortical laterality, possibly through selective activation of cortical motor centres on the preferred side.